Velocity-selection-type pickup tube



Feb. 13, 1951 G A, MORTON 2,541,374

VELOCITY-SELECTION-TYPE PICKUP TUBE Filed June 28, 1946 /20 z#20 n Ll.

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afar/Paw Vilac/nfs /A/ voz rf T0 Patented Feb. 13, 1951 2,541,374 VELOCITY-SELECTION-TYPE PICKUP TUBE George A. Morton, `Princeton, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application June 28, 194e, serial No. 679,929

4 Claims.

This invention relates to electron tubes and particularly to tubes in which the electrons emitted by the target are separated into relatively high and low velocity streams and either the one or the other is utilized for production of an image or other signal indication, and is an improvement of the electron tube disclosed in my joint application with Gardner L. Krieger, filed June 28, 1946, Serial No. 679,928.

It is an object of the invention to provide an electron pick-up tube in which the electrons emitted by a screen are velocity-selected.

It is another object of the invention to provide an electron pick-up tube for transmitting to a distant point electric current which varies in accordance with the velocities of the electrons emitted by the scanned elemental areas of the target; on which an image is focused.

Another object of the invention is to provide an electron pick-up tube in which the target is Scanned by a cathode ray beam for production of electrons, varying the velocities of the electrons in accordance with a potential image thereon and selecting electrons of predetermined velocity range for multiplication.

Other objects of the invention will appear in the following specification, reference being had to the drawings, in which:

Figure l is a section through a tube of the invention.

Figure 2 is a section through a tube of a modii'lcation.

Figure 3 contains graphs of the velocity distribution of electrons at the selector grid.

Referring to Fig. l of the drawing, the tube by Way of example I have illustrated a target whose resistance is varied by incident radiation from an'object to be televised. This target consists of a body made of a sheet of material having a positive or negative resistance characteristic, depending upon the desired method of operation. For photo images it may be made of a photo conductor, such as activated thalium sulphide, copper oxide, etc., particularly for' incident radiation of near infrared, visible light or ultraviolet energy. VFor far infrared or heat energy incident thereon, the target may bemade of a thermo-sensitive material such as thin glass, the titanates of barium and strontium, titanium oxide or other suitable material. All these materials have a negative coeflicient of resistance. Composite iilms can be processed to exhibit a positive coefficient of resistance with change in temperature. That is, metals may be combined with the materials having negative coeicients of resistance to obtain a target of positive coefcient. It is also a known phenomenon that titanium oxide (T1203) has a critical temperature below which it has a positive coeflicient and above which it has a negative coefficient. This can be used either alone or in combination with other materials for the resistance body.

On the side of the target body 4 facing the end of the tube is a very thin conducting film 5, which may be transparent-l to the radiant energy utilized, as when ythe sensitive layer is a photo conductor, or it may convert radiation to heat, which is conducted to the sensitiveV layer. On the opposite surface is placed a sensitive mosaic 5 of small discrete areas capable of emitting primary electrons, photoelectrons, or secondary electrons. By Way of example, in Fig. 1 a target has been shownV capable of emitting secondary electrons under bombardment of the cathode ray beam from gun G. This gun may be of standard construction, such as disclosed in the application of Paul K. Weimer, filed September 16, 1944, Serial No. 554,494, now U. S. Patent 2,433,941. The cathode may be connected `to the negative terminal of the voltage supply. rThe beam from the Vgun passes through an appropriate aperture 'l in the electrode 2. When 'using the gun for bombarding secondary electrons from the target, the sensitive discrete areas constituting the mosaic of the target may be silver-magnesium alloy, for example.

Between the target T and the electrode 2 are lplaced a plurality of electrostatic ring electrodes, such as 8, 9 and I0. These are for accelerating the electrons emitted by the target to the electrode 2. Closely adjacent the electrode 2 on the opposite side is a selector electrode II, shown in the form of a screen or grid. Beyond this grid, and opposite the aperture'S, is placed the iirst dynode I2 of an electron multiplier. As many stages of multiplication as desired may be used, but I have shown additional dynodes I3, I4 and I5 and a collector i6 of a four-stage multiplier. Any form of multiplier may be used and the one illustrated is diagrammatic only.

To scan the beam from gun G over the mosaic o the target T, and also to scan the secondary electrons emitted by the target T over the diaphragm 2 for successive passage of electrons through the aperture 3, I provide a deecting coil unit I1, which may have the usual two coils arranged at right angles, commonly referred to as vertical and horizontal deection coils, connected to a saw-tooth or other generator (not shown). These are well known and the illustration is diagrammatic only. Around the deflecting unit is placed the electromagnetic focusing coil I8 for producing a uniform magnetic field for focusing the beam electrons on the mosaic and the bombarded secondary electrons 'emitted by the target on the diaphragm 2.

At the target end of the tube I may be placed the unit I9 for projecting an image of an object on the target through the end of the tube by light, infrared, thermal, or other desired incident energy. Assuming, by way of example, that thermal energy is to be used to produce the image of the object on the target, the end 20 of the tube may be made of silver chloride, so that the thermal energy will pass sufficiently through to the target. This end 20 is suitably sealed to the envelope I to form a vacuum-tight joint. The lenses may be made of rock salt, for example.

Lifter plates 2|, 22, such as disclosed in Iams Patent 2,213,177, August 27, 1940, separate the beam electrons from the secondary electrons accelerated from the target mosaic to the anode 2. These would be connected to direct current potentials, as will be understood by those skilled in the art.

The positive terminal of the direct current voltage supply may be connected to ground and various potentials may be applied te the other terminals, as would be understood by those skilled in the art. However, I have indicated suitable potentials on the drawing by way of example.

Assume that the target T is being scanned by the beam from gun G and that no radiant energy1 is incident on the target. The areas while under beam impact will emit secondary electrons substantially uniformly, but the electrons will be emitted with a range of velocities, as indicated by graph A. These secondary electrons are accelerated toward the electrode 2, producing uniform current flow through the target body 4. If there are 1L elemental areas of the mosaic, one can visualize n electrical resistance paths transversely across the target body 4 and there will be a voltage drop in each path equal to the resistance times the electron current. No radiation being incident on the target T, the plurality of paths have the same resistance and the electron currents therealong will be substantially uniform. The elemental areas will thus have the same potential, but the velocities at the selector grid II of electrons emitted by each elemental area will have the range or velocity distribution shown by graph A of Fig. 3.

The potential on selector grid II is adjusted to a potential such that all electrons having a velocity below V1 of graph A cannot pass grid II and substantially all the electrons emitted are reflected and collected by the various electrodes between the anode 2 and the target T. The multiplier output from collector IB will then be zero.

Now, assume that an image of an object is produced on the target by incident thermal energy. Since the target bedy l has a negative coefficient of resistance, the resistance of the body il in the multiplicity of paths now becomes less, the resistance of each path depending upon the amount of energy incident upon the area through which the path passes. Each path will have a voltage drop equal to the resistance times the electron current, the white areas thus having lower potentials than the gray areas and the gray areas less than the black areas. Thus, there will be a potential image over the mosaic corresponding to the image produced by the incident thermal energy. The velocity distribution at the selector grid II for areas receiving no incident energy (black areas) will, as before, be that given by graph A of Fig. 3, because the potential of these areas did not substantially change. The electrons emitted from areas receiving the most thermal energy (whitefareas) are more negative to the grid I I and their velocities relative to it are given by graph B. Those areas receiving intermediate amounts of energy will be intermediate the values of graphs A and B, such as shown by graph C.

All electrons having velocities above the value V1 pass through aperture 3 and the selector grid Il to the rst dynode I2 and the total number passing through the selector for the white areas is proportional to the area V1Q1V2. For areas receiving intermediate incident energy (gray areas), the energy input to the multiplier is indicated by area V1Q2V3. For areas receiving no thermal energy, the multiplier input will be zero. Thus, the input and output of the multiplier varies with the incident energy on the target.

The field of deecting unit I'I scans the electrons emitted by the mosaic through the aperture 3, as in the known dissector tube. 'I'he image on the target is dissected Iand the multiplied signals, with or without amplification, may be transmitted from the collector electrode I6 to any desired point for reproduction of the image in known ways.

In Fig. 1 the aperture 3 may be of such size as to deiine the picture elements, or the beam spot may define it and the aperture 3 may be made larger than the size of a picture element.

In the modification of Fig. 2, the electrons emitted by the target mosaic or sensitized screen are photoelectrons instead of secondaries. These are produced by ultraviolet energy from a lamp or generator 23, such as a mercury lamp of ring or semicircular shape, or other radiation which does not conflict with the radiation being imaged. The scanning coils and focusing coils may be divided into two parts 24, 25 and 26, 2l', respectively, so the lamp may be placed in position to project its rays into the tube. The anodes 8, ii

. and IIB may be sand-blasted to produce diffused reflection of the ultraviolet rays to the mosaic surface 6, which in this case may be activated manganese, potassium or caesium.

In this modification I have shown, by way of example only, a construction in which the low velocity electrons are selected and utilized. This is accomplished by operating an electron mirror 28 at some potential that will collect all electrons having a volt velocity equal to, or greater than, V4 in Fig. 3. The lower velocity electrons scanned through aperture 3 cannot land on the mirror and are reflected to the first dynode I2. Electron multiplication is accomplished in the way described in `connection with Fig. 1. The higher velocity electrons land on mirror 28 and are not utilized. The number of electrons passing into the multiplier in this case is given by the area V4Q3V5 for the white areas. The multiplier input for an area having incident energy of some particular value between black and white would be given by graph D and the number of electrons in the multiplier input is given by the area V4Q4Vs.

The various parts of Fig. 2 that are similar to those of Fig. 1 have been given the same reference characters and they need not be described in detail.

I claim:

1. An electron discharge device comprising, an envelope, a target electrode mounted within said envelope, said target electrode formed of a radiation sensitive material having a specific electrical resistance which is a function of radiant energy impinging thereon, a conductive electrode in contact withone surface of said target electrode, an electron emissive material on an opposite surface of said target electrode, a collector` electrode within said envelope, and a selector electrode mounted between said collector electrode and said target electrode, means including an electron gun for initiating an electron emission from said electron emissive target material, leadl means connected to saidr conductive electrode for joining said conductive electrode to a source of potential, electrode means within said envelope for accelerating electrons from said emissive target coating toward said collector electrode, means for focusing radiation from a source of radiant energy upon said target electrode for changing the specic resistance of said target material, and lead means connected to said selector electrode for joining said selector to a second source of potential for blocking the electrons from those portions of the emissive target coating inicontact with the target portions not subjected to radiations from said source of radiant energy.

2. An electron discharge device comprising, an envelope, a target electrode mounted within said envelope, said target electrode formed of a radiation sensitive material having a specic electrical resistance which is a function of radiant energy impinging thereon, a conductive coating on one surface of said target electrode, a secondary electron emissive material on an opposite surface of said target electrode, a collector electrode within said envelope, and a selector electrode mounted between said collector electrode and said target electrode, an electron gunmeans for forming an electron beam along a path intercepting said target electrode, means for scanning said electron beam over the surface of said secondary electron emissive material to initiate a secondary emission from said target, lead means connected to said conductive target coating for joining said Acoating to a source of potential, electrode means within said envelope for accelerating secondary electrons from said emissive target coating toward said collector electrode, means for focusing radiation from a source of radiant energy upon said target electrode for changing the specic resistance of said target material, and lead means connected to said selector electrode for joining said selector to a second source of potential for blocking electrons from those portions of the emissive target coating in contact with target portions subjected to radiations from said sourc of radiant energy. c

3. An electron discharge device comprising, an envelope, a target electrode mounted within said envelope, said target electrode formed of a radiation sensitive material having a specific electrical resistance which is a function of radiant energy impinging thereon, a conductive coating on one surface of said target electrode, a photosensitive material on an opposite surface of said target 5 electrode, a collector electrode within said envelope, and a selector electrode mounted between said collector electrode and said target electrode, means for initiating emission from said photosensitive target material, an apertured plate electarget electrode, means scanning said photoemission over said apertured plate electrode, lead means connected to said conductive target coating for joining said coating to a source of potential, electrode means within said envelope for accelerating electrons from said photoemissive target material toward said collector electrode, means for focusing radiation from a source of radiant energy upon said target electrode for changing the specific resistance of said target material, and lead means connected to said selector electrode for joining said selector to a second source of potential for blocking electrons from those portions of the photoemissive target material in contact with target portions not subjected to radiations from said source of radiant energy.

4. An electron discharge device comprising, an envelope, a target electrode mounted within said :3io envelope, said target electrode formed of a radiation sensitive glass material having a specific electrical resistance which is a function of radiant energy impinging thereon, a conductive coating on one surface of said target electrode, an electr-on emissive material on an opposite surface of said target electrode, a collector electrode within said envelope, and a selector electrode mounted between said collector electrode and said target electrode, means for initiating emission from said electron emissive target material, an apertured diaphragm electrode positioned between said collector electrode and said target electrode, means for scanning said electron emission over the surface of said apertured diaphragm electrode, lead means connected to said conductive target coating for joiningsaid coating to a source of potential, electrode means within said The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,159,568 Ploke s May 23, 1939 v2,213,175 Iams Aug. 27, 1940 2,288,402 Iams June 30, '1942 70 2,412,086 Hallmark Dec. 3, 1946 Larson Jan. 18, 1949 trode positioned between said collector and said i envelope for accelerating electrons from said 

